The invention relates to a recirculating ball nut and an assembly for a ball screw drive. The invention further relates to a method of manufacturing a recirculating ball nut.
Ball screw drives are employed in power steering systems in vehicles, for example. The recirculating ball nut is mounted on the steering linkage of the vehicle, the recirculating ball nut being held stationarily in the longitudinal direction of the steering linkage and mounted for rotation in relation to the steering linkage. Concurrent threads are provided in the recirculating ball nut and on the steering linkage. Provided between the recirculating ball nut and the steering linkage are transmission means, for example balls, which engage in both threads and in this way couple the recirculating ball nut and the steering linkage to each other. When the recirculating ball nut is rotated relative to the steering linkage, for example by a belt drive engaging the outer periphery of the recirculating ball nut, the steering linkage is shifted relative to the recirculating ball nut in the longitudinal direction by means of the balls. This allows the ball screw drive to apply an additional steering force on the steering linkage, for example.
In order to ensure both as effective a steering force assistance as possible and a reliable force transmission from the drive to the steering linkage, it is required that the recirculating ball tracks be manufactured with a very low manufacturing tolerance, so that the balls have a very small play in the recirculating ball tracks while they can still roll in the recirculating ball tracks with low friction. Until now, forging methods have been used for manufacturing the recirculating ball nuts; the known forging methods do not ensure a sufficient precision for the manufacture of the ball tracks, or a very great manufacturing effort is involved in reaching the desired precision. In addition, the internal recirculating ball tracks are difficult to access, which increases the manufacturing effort. Alternative manufacturing methods such as milling feature the drawback that very large amounts of materials are required.